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    <title>Document</title>
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    <script>
        // 面试题：
        // 闭包：内层函数引用外层函数中的变量的集合
        // 闭包=内层函数+外层函数的变量
        function out() {
          let a = 10
          function innner() {
            console.log(a)
          }
          innner()
        }
        out()
      </script>
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